Genetic rearrangement is somatic cells may be an important mechanism contributing to a cell's malignant potential. Evidence suggesting that oncogenes may be activated by translocation and the association of multiple human malignancies with a specific karyotypic abnormalities supports this concept. However, little is known about the mechanisms that are involved in molecular rearrangement or genetic recombination. Employing mutants of Herpes Simplex Virus (HSV) as probes it is possible to develop an assay system for genetic recombination in eukaryotic cells, and compare normal cells with those derived from patients having abnormalities in DNA repair pathways. Recombination between Herpes Simplex Virus (HSV-1) mutants having nonoverlapping complementary mutations in the thymidine kinase or DNA polymerase loci can be quantitated. These studies will determine if genetic recombination between co-infected HSV-1 is modulated by prior DNA damage to human cells. The effect of inhibitors of macromolecular synthesis (protein synthesis and transcription of mRNA) on genetic recombination will contribute to our understanding of whether this is an inducible phenomenon in human cells. Modifiers of cell function such as protease inhibitors, 3- aminobenzamide and phorbol esters modulate sister chromatic exchange and may affect DNA repair pathways. We will determine if these agents modulate genetic recombination by comparing the level or recombination in cells pretreated with either of these agents, with untreated cells. These studies may help elucidate those cellular pathways that are important for the expression of genetic recombination. In studies quantitating genetic recombination on host cells from individuals with specific DNA repair disorders (e.g., Bloom Syndrome, Fanconi's anemia) will determine whether either or both of these mutants express levels of recombination different from that observed in normal cells. The effects of specific forms of DNA damage to these cells on genetic recombination will be determined, along with the effects of protease inhibitors and 3- aminobenzamide in this setting. To determine if those cell exposures previously identified as recombinogenic are associated with expression of a mutator phenotype we will employ an assay for mutagenesis that measured reversions of ts mutants of HSV-1 to the ts+ (non-temperature sensitive) phenotype.